Actually this is not that unusual. You should find that pretty much when this happens, the person had been drinking heavily & effectively was quite "loaded" (ie,the reason why the person collapsed to begin with; plain drunkenness). Such phenomena has been found to help protect critical tissues from freeze damage & a form of such idea is used in the cryogenic preservation/preparation process (ie, typically a form of glycerin is employed).

Extreme cooling of the body greatly aids survivability as a search of the NDE reports (particularly on IANDS) should reveal that drowning victims were recoverable even well after being submerged in extremely cold water for 20 minutes and more !